The Collaborative International Dictionary of English v.0.48:

mousetrap \mouse"trap`\, mouse trap \mouse" trap`\, n.
   Any device that catches, and usually kills, mice. They are of
   various designs, the most common being a stiff loop of wire
   mounted on a small wooden platform base and attached to a
   strong spring, which holds the loop firmly against the base.
   To activate the trap, the loop is pulled through a 180[deg]
   arc against the tension of the spring and held against the
   base by a delicate metal catch, which can keep the loop from
   moving, though in a state of high tension. The metal catch is
   moved when a mouse tries to take a piece of bait attached to
   it, releasing the loop which forcefully moves though an arc,
   usually killing the mouse. A larger version of the same
   device is used as a rat trap.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mousetrap
    n 1: a trap for catching mice
    2: (American football) a play in which a defensive player is
       allowed to cross the line of scrimmage and then blocked off
       as the runner goes through the place the lineman vacated
       [syn: mousetrap, trap play]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "mousetrap":
   Dionaea, Mark, baited trap, bazooka, booby trap, calliope,
   deadfall, deathtrap, decoy, firetrap, flytrap, gin, hedgehog,
   launch pad, launching pad, launching platform, launching tube,
   mine, mole trap, pitfall, projector, rattrap, set gun, silo,
   spring gun, springe, trap, trapfall